Various antifoggants are commonly used in order to prevent fogging of a silver halide photographic material. For example, heterocyclic compounds, especially the heterocyclic compounds having mercapto groups, are well known as the antifoggants. These compounds reduce the fog caused during development and storage, but have the problem that sensitivity is lowered. Accordingly, these compounds can not be relied upon when a high sensitivity is required since the reduction of a fog also results in the deterioration of the sensitivity. Further, the problem that the photographic light-sensitive material is desensitized during storage can not completely be avoided.
One of the methods for solving these problems is disclosed in JP-A-62-174742 (the term "JP" as used herein means an unexamined published Japanese patent application) and JP-A-62-174743, in which the compounds having a mercapto group are incorporated into light-insensitive layers. However, the combined use thereof with a cyanine dye, particularly a cyanine dye having a sulfoalkyl group, is insufficient when high sensitivity is required and the reduction of a fog is accompanied by a lowering of sensitivity.
In general, sensitization of a silver halide emulsion can be carried out by methods such as noble metal sensitization, sulfur sensitization, reduction sensitization, and the addition of a development accelerator. However, these methods cause an increase in fog, and therefore the above antifoggants have not been able to lower a fog to a satisfactory level because of the decrease in a sensitivity.
Further, a method for preparing a silver halide emulsion having a high sensitivity and an excellent developability is disclosed in JP-A-63-305343. In that method, chemical sensitization is carried out in the presence of a silver halide-adsorbing compound such as a sensitizing dye or a photographic characteristics stabilizer in order to control the characteristics of the silver halide grains so that the development is initiated from the peaks of the respective grains. However, this method has the problems that an excessive use of the sensitizing dye causes a stain by the dye remaining after development processing and that an excessive use of the photographic stabilizer results in difficulty in carrying out spectral sensitization thereafter.
One of the methods for solving these problems is disclosed in JP-A-2-167539, in which two kinds of dyes are used. But this method was insufficient for achieving high sensitivity.